1. Field of the Invention
This invention describes a method of using x-rays to inspect an object or a parcel.
2. Description of the Related Art
X-ray scanners are used for baggage screening as at the airports, for inspection of parts in industrial use, for inspection of food cans by the food industry, and for any other inspection use. A simplified sketch of the conventional x-ray scanner is shown in FIG. l. It uses a single x-ray source 60 which is placed below and to one side of the tunnel 90 as shown. A fan beam 64 from the source 60 then passes through the object or baggage inside the tunnel and impinges on the “L” shaped detectors 611 and 612 which are housed in detector electronic boxes 613 and 614 respectively. The image produced by such a scanner is 2D and lacks the detail needed to inspect the 3D volume of the object.
Therefore, to inspect the 3D volume, CT (Computed Tomography) or CAT (Computed Axial Tomography) systems are used. However these systems are not in wide use, as they are large, expensive, consume large power and need heavy duty cabling to be first installed in the room, and are not portable. Therefore to fill the gap between 2D scanners and the 3D CT systems, multi view systems have been developed.
A simple multiview system with two views is shown in FIG. 2, and another system with two sources and six views as described in U.S. Pat. No. 7,319,737 B2 (Singh), is shown in FIG. 3. In FIG. 2, for the purposes of brevity, only the electronic boxes are shown. In comparison to FIG. 1, two additional boxes 513 and 514 are shown in FIG. 2. As is well known to a person skilled in the art, these would correspond to a second x-ray source placed on the other side of the tunnel across from the first source 50 of FIG. 1. The width 100 of the detector electronic boxes 613, 614, 513, 514 is usually in the range of twelve to fifteen inches. The addition of extra detector electronic boxes 513 and 514 makes the length 101 of the tunnel 90 longer.
Since the images produced from just two views is not sufficient to provide detailed information of a 3D object, more than two view systems have been developed. These multiview systems are three to five view systems. As would be apparent to a person skilled in the art, the addition of third or more views leads to adding more of detector electronic boxes to the system of FIG. 2. This leads to a large length of the tunnel which makes the system big. Such big systems are therefore not in use for the inspection of carry on baggage at check points in buildings or at airports where a small footprint is needed.
The problem becomes further worse for a system of FIG. 3 which uses slant beams that require detector electronic boxes to be positioned at oblique angles and where the separation between two adjacent detectors may be much less than twelve or fifteen inches needed to accommodate such wide electronic boxes that the current technology offers. The system of FIG. 3 uses two x-ray sources 50 and 60. The beams 54, 55 and 56 are associated with the first source 50, and are detected by detectors 51, 52 and 53 respectively. Likewise, the beams 64, 65 and 66 are associated with the second source 60, and are detected by detectors 61, 62 and 63 respectively. If such a system were to use wide electronic boxes of FIG. 1 or FIG. 2, the system of FIG. 3 would become very large and impractical for use in office buildings or where smaller footprint is needed.
The objects of this invention are therefore to overcome some of the above problems and are listed next.